What's your hang height? With that piece of info, we can figure out the PPFD level.
LED's produce photons, same as a match, the fusion reaction from the sun, or an HPS fixture. Sure, the photons are different frequencies and have a different mix but a photon is a photon. LED's don't heat the plants because they don't generate any/much IR but, other than that, it's just photons.
The thermometer indicates that your temperature is 69.8° and RH is 39%. Your VPD is good but, at that temperature, growth slows significantly compared to, say 10° warmer. Is that a concern for you?
Cannabis will thrive at 800-1000µmols if there are no other limiting factors. Seeing that your PPFD is well below that, the symptoms that you're seeing are: not an issue off too much light, due to an issue with the plants themselves; or due to something in your grow environment.
First off, that's a
gorgeous canopy.
What symptoms are you seeing that indicate too much light? From the photo that you've posted, it looks like many of the leaves are light green. I'm no expert on nute issues but, IIRC, that's a symptom of not enough N.
Re. plants being the issue - that' not likely if the issue is widespread.
Light is one issue but there are eight other factors that make up the grow environment. If you run through them in turn, you should be able to find the culprit. A grower on another forum was in a situation similar to yours. After lots of back and forth, he figured out that he had watered his plants incorrectly. The bottom few inches of dirt in his plant pots had hardened and his roots were drowning. After he dealt with that, he was able to almost double his light levels.
RE. getting a cheap PAR meter. The SF 4000 emits light at wavelengths >= 660nm. The inexpensive meters on Amazon that share the "Active Eye/Hydrofarm LGBQM quantum sensor" are not able to read light with a wavelength > 660nm. Given that, they cannot read PAR. Second, since the SF 4000 has light at >= 660nm, if you purchase a device that uses that sensor, you'll want to correct the reading you get from those meters.
I've tested the Uni-T lux meter against my Apogee with the Vipar Spectra XS-1500 and the Growcraft veg light and, when I use the Uni-T, the factor of 0.015 gives me accurate PPFD readings . The spectrum of the SF 4000 is similar enough to the XS 1500 to use the 0.015 factor.
